1. Field of the Invention
The present invention relates to an image forming apparatus, and in particular, relates to an image forming apparatus which forms an image on a medium using an ink ribbon including ink of a plurality of colors.
2. Description of Related Art
Conventionally, an image forming apparatus which forms an image on a transfer medium such as a transfer film and an image carrier and a printing medium such as a card, sheet, and tube has been widely known. In such an image forming apparatus, an indirect printing method in which an image (mirror image) is formed on a transfer medium using an ink ribbon and then the image formed on the transfer medium is transferred to a printing medium and a direct printing method in which an image is directly formed on a printing medium using an ink ribbon is adopted, for example.
In such an image forming apparatus, color printing is generally performed by generating a color image by superimposing images, each formed with corresponding color of the ink. That is, color printing is performed by superimposing images, each formed with corresponding color of the ink (e.g., ink of Y (yellow), M (magenta), and C (cyan)), on a medium (transfer medium for the indirect printing method, printing medium for the direct printing medium) in accordance with printing data (e.g., printing data of each of Y, M, and C) to which input printing data or input image data is converted and printing the superimposed image.
In color printing, when printing positions of images of each color of ink on a medium are deviated, a color image printed on the medium gets blurred, resulting in deterioration in printing quality (image quality). The phenomenon that printing positions of images of each color of ink are deviated is generally called color deviation. Various technologies for correcting printing positions of images of each color of ink are disclosed.
For example, technologies are proposed such as to reduce correcting time by printing density correcting pattern and color deviation patter on an intermediate transfer belt (see Japanese Patent Application Laid-Open No. 2008-3396), to perform resist adjustment using an unused region which is not used for image printing among an image formable region (see Japanese Patent Application Laid-Open No. 2010-204547), and to perform cueing a transfer medium and an ink ribbon after nipping a thermal head and a platen in a state that a mark formed on a transfer medium is located at the upstream side of a sensor (see Japanese Patent No. 5848129).